Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only give destructiveHint=true and a title, so the description carries real weight here. The leading "WRITE:" marker and the duplicate-entry warning disclose the key behavioral risk (repeat calls create additional running entries), which the annotations do not express.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the WRITE marker and the primary warning. No filler; the API endpoint note is a compact trailing detail.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 5-param, single-required-field write tool with no output schema, the description covers the essential risk and timing modes. It leaves open what happens if the user already has a running timer, which would be the one useful addition.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 80%, so descriptions already document task_id, user_id, start_time and start_time_timezone. The description adds only the "now or at a given time" framing for start_time and nothing about the timezone dependency, so it sits at the baseline for high-coverage schemas.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource (start a timer for a user) plus the two timing modes (now or at a given time). It is clearly separable from timetac_stop_time_tracking and timetac_create_time_tracking, though it doesn't name those siblings explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

"Each call can create a new running entry, so do not repeat it" is an explicit, actionable warning against duplicate invocation. It stops short of naming alternatives (e.g., check timetac_current_time_trackings first, or use stop_time_tracking to end one).

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.